Communication techniques between electronic devices are advancing in various ways. In particular, with advances in communication technologies for portable terminals and introduction of Internet connectivity, communication between electronic devices including portable terminals is utilized for many purposes.
Wi-Fi communication is a Wireless Local Area Network (WLAN) technology. WLAN provides a communication service such as Internet to portable terminals (e.g., smart phones, tablet PCs, Personal Digital Assistants (PDAs), notebook computers, etc.) traveling within a certain distance from an installed Access Point (AP) which is a wireless access device. WLAN technology had a short propagation distance of about 10 m in the early stage but has recently greatly expanded the propagation distance up to 50 m˜hundreds of meters. Data transfer rates in WLAN have also improved to transmit and receive high-volume multimedia data.
The advance of Wi-Fi communication has enabled the development of a Wi-Fi Direct technique which allows print and content sharing through free communication between Wi-Fi devices without an AP or a router. Wi-Fi Direct, which is also referred to as Wi-Fi Peer-to-Peer (P2P), can operate by grouping a P2P group owner and a P2P client.
A protocol emerging in this field, called Wi-Fi Display communication, is a technique for sharing data including a video stream and/or an audio stream between Wi-Fi enabled electronic devices. For example, a Wi-Fi Display source electronic device (hereafter, “source device” or just “source”) transmits a video stream and/or an audio stream to a Wi-Fi Display sink electronic device (hereafter, “sink device” or just “sink”). The two devices share the streams and simultaneously output the streams through a screen and/or a speaker. In Wi-Fi Display communication, connectivity is achieved using, for example, Wi-Fi Direct.
Herein, a source device denotes a device transmitting the video stream and/or the audio stream, and a sink device denotes a device receiving the video stream and/or the audio stream.
A standard for the Wi-Fi Display communication is described in a Wi-Fi Display specification defined by the Wi-Fi alliance, which is a consortium of companies and entities establishing wireless protocols.
The Wi-Fi Display communication for transmitting data from the Wi-Fi Display source device to the Wi-Fi Display sink device includes Wi-Fi Display (WFD) device discovery, WFD connection setup, WFD capability negotiation, and WFD session establishment. Besides these, the WFD communication can further include a plurality of selective operations such as link content protection.
When the WFD session is established, data is transmitted from the WFD source device to the WFD sink device.
WFD session establishment, and the stream transmission from the WFD source device to the WFD sink device, will now be explained. The WFD source device decodes an encoded stream which is stored therein or received from another medium such as Internet, and outputs the decoded video stream through the screen and the audio stream through the speaker. Herein, encoding refers to at least compressing of the video stream and/or the audio stream. For example, the video stream is compressed in the format of Moving Picture Expert Group (MPEG)-4 of International Standard Organization (ISO)-International Electronic Commission (IEC) or H264 of International Telecommunications Union-Telecommunication standard sector (ITU-T), and the audio stream is compressed in the format of Linear Pulse Coded Modulation (LPCM) 44.1, LPCM 16-48, Advanced Audio Coding (AAC), AC-3, Authentication, Authorization, and Accounting (AAA), Adaptive Multi Rate (AMR), Windows Media Audio (WMA), MPEG-2 Audio, or MPEG-4 Audio.
The WFD source device encodes the raw streams (e.g., video stream and audio stream) that have been decoded and output through the screen/speaker, and transmits the newly encoded stream to the WFD sink device. The WFD sink device decodes the encoded stream received from the WFD source device, and outputs the video stream through the screen and the audio stream through the speaker. Hence, the WFD source device and the WFD sink device share the audio and video streams.
Thus, the WFD source device decodes the encoded stream stored therein or received through another medium such as Internet, outputs the audio/video streams through the screen/speaker, and re-encodes the streams in order to transmit the output raw stream. However, encoding the video stream is time consuming. The video stream requires an encoding time about 10 times that of the audio stream, which may differ according to performance of a hardware encoder or a software encoding module. In a camera application, a portable communication terminal, which is an example of the WFD source device, often captures an image using an embedded digital camera When taking a video, a large number of images are captured using continuous shooting. With the large amount of data generated, encoding is necessary to store or send the captured images to another person. As the portable terminal frequently uses the encoder (or the software encoding module) for encoding images and the amount of the image data to process increases, this puts a strain on device resources.
Hence, in the WFD communication, it is required to address the much encoding time of the WFD source electronic device by modifying the method of the WFD source electronic device for decoding the encoded video stream, outputting the raw video stream through the screen, and re-encoding and transmitting the output video stream.